The invention relates to a twisting device for electrical conductors a method therefore according to the disclosed embodiments.
A method for twisting electrical or optical conductors such as wires, cables, cable bundles, waveguides, etc., in a twisting device with two counter-rotatable twisting heads is disclosed in WO2013068990A1. The conductors are drawn into the twisting device between the twisting heads one after the other and the distance between the twisting heads is reduced as the twisting process progresses, preferably as a function of the number of revolutions of the twisting heads, in order to compensate for the overall shortening of the twisted conductors as the twisting continues. Advantageous variants provide for gradually increasing the rotating speed of the twisting heads in a first phase of the twisting process and then gradually reducing the speed in a second phase of the twisting process, or also increasing and reducing the rotating speeds of the twisting heads separately, or twisting them according to programmable speed profiles.
Significant problems associated with such methods include the lengthwise variability of the individual conductors, tolerances due to conductor transfers in the machine, temperature fluctuations and tolerances in the external diameter of the conductor. The quality of the twisting also depends on the force that is applied when twisting in the conductor axis. It is extremely difficult to apply a constant force to the conductors corresponding to the shortening profile when twisting in an automated process. Such an arithmetical (theoretical) determination of the shortening profile must be adapted individually for each twist in order to preclude the disturbance variables.
This also applies for a device such as the one disclosed in EP1032095B1, in which the intention is to regulation the shortening profile. The conductor is clamped in place on both sides, a force sensor on a fixed gripper is applied. A twist rotor is fitted movably and travels over the shortening of the conductor, synchronised as closely as possible with the actual shortening of the conductor, wherein its position is regulated taking into account the measured force. The tensile force is calculated at the fixed-position conductor terminal, and the advance path of the twisting motor is regulated from this. This solution requires very fast signal processing. Even so, the force fluctuates by a predetermined value in the control process, and the reaction must be delayed because the process is extremely dynamic, so it is very difficult to compensate for an error. It is almost impossible to maintain an exact tensile force, and this too can lead to a high reject percentage. This applies particularly for short conductors for twisting, since they have scarcely any axial damping effect; an extremely large amount of effort must be applied for control.
Another group of machines, the “semi-automated conductor twisters”, work in the area of the conductor shortening against a permanent force, which is typically applied pneumatically. Quality monitoring would only be possible with the investment of considerable sums of money due to the long shortening paths. This issue is not particularly important for manual processing, because the operator sees each conductor in production and so is able to detect faults quite effectively
Similar problems to those stated above also arise in stranding. Thus for example DE19631770A1 discloses a stranding machine in which prepared conductors are clamped by hand. The two conductors are stranded by rotating both conductors starting at the conductor ends secured in the twisting head and at the same time with a controlled twisting shuttle process, so that the distance between the twisting shuttle and the twisting head becomes larger as the process continues. In this process, it is the conductor sections located between the twisting shuttle and the twisting head that are twisted. Document DE19631770A1 also describes how the twisting clamp mountings are arranged so as to be displaceable along the linear guides by means of a forward motion device, e.g., a pneumatic cylinder with counter-pressure control. This forward motion device with pneumatic cylinder and counter-pressure control, mounted under the twisting head with the twisting clamp mountings travels along the entire shortening path that is created by twisting.